The present invention relates to fluid supplies for inflatable vehicle occupant restraint systems, and more particularly, to a filter pack for use therein and a method for assembling the filter pack in the fluid supply.
In general, vehicle occupant restraint systems utilize some type of crash sensor which senses the rapid deceleration which occurs when the vehicle is involved in a collision. The collision signal from the sensor actuates a fluid supply which provides a quantity of inflation gas to inflate an expansible confinement and restrain the vehicle occupant. Restraint systems of the class described may be positioned in the dashboard for deployment in the passenger compartment of the vehicle or may have the fluid supply and confinement portion located on the steering wheel to restrain the driver. In the latter case, it is necessary that the fluid supply fit compactly adjacent the steering wheel hub, without extending too far toward the driver, or radially toward the rim of the steering wheel. Therefore, while the present invention is equally adapted for many occupant restraint systems, it is especially useful for such a system which is located on the steering wheel, and will be described in connection therewith. It is also well adapted for systems which utilize the combustion of solid gas-generating materials as the source of the inflation gas, especially when such gas generating materials produce gaseous combustion products including both the generating gas and particles of varying sizes.
Among the prior art fluid supplies for occupant restraint systems are those exemplified by German Pat. No. 2,325,310, in which the generated gas flows radially out of a cylindrical housing. Another type of fluid supply is exemplified by U.S. application Ser. No. 459,529, filed Apr. 10, 1974, now Pat. No. 3,984,126, and assigned to the assignee of the present invention, showing a generally cylindrical housing from which the generated gas flows axially out of one end of a cylindrical housing. Among the common features of most such prior art fluid supplies are the inclusion of a mass of combustible gas generating material and some type of filter disposed between the combustible material and the fluid discharge ports defined by the housing.
Among the problems associated with the prior art fluid supplies has been the tendency for the filters to become clogged with the fine particles of fly ash which comprise a certain, relatively small percent of the combustion product when the gas generating material burns. If sufficient clogging of the filter occurs, the flow area through which the generating gas is discharged may be restricted to the point that excessive pressure builds up within the housing, thus presenting the possibility of the fluid supply exploding rather than directing a controlled flow of inflating gas into the confinement.
Another problem relates to the phenomenon of "channelling" which occurs whenever a gap exists between the filter pack and either the outside wall of the fluid supply or the central support member. Such a gap permits a fow of the generated gas to pass around rather than through the filter, carrying hot combustion particles which may then pass through the fluid discharge port into the inflatable confinement, causing damage to the confinement and, possibly, injury to the vehicle occupant.